Remote controlled unmanned vehicles are well known for use in military and police surveillance, bomb disposal, disaster investigation, and the like. Most commonly these UMVs are unmanned ground vehicles (UGV) which have the ability to travel only along the ground, or unmanned aerial vehicles (UAV) which have the ability to travel only in the air.
Aerial vehicles, commonly electric battery powered hovering vehicles with spinning rotors for lift and propulsion, have the ability to access elevated areas like windows and roof tops and provide a wide range of observation, but have a limited operating time due to the high energy requirements of flight and the weight of batteries. Such an aerial vehicle is disclosed for example in U.S. Pat. No. 7,510,142 to Johnson.
Ground vehicles have a much longer operating time but have difficulties accessing elevated areas, and maneuvering over stairs and like obstacles. Such a ground vehicle is disclosed for example in U.S. Pat. No. 6,144,180 to Chen et al.
Due to the limitations of such a single travel mode, UMVs have been developed which have the capability to travel both in the air and along the ground. For example U.S. Pat. No. 8,205,820 to Goossen et al. discloses an aerodynamic flying assembly comprising an unmanned aerial vehicle integrated with an unmanned ground vehicle A power unit and controls are shared by the unmanned aerial vehicle and the unmanned ground vehicle, and a disengagement mechanism separates the unmanned ground vehicle from the unmanned aerial vehicle for ground operations.
U.S. Pat. No. 6,588,701 to Yavnai discloses a remotely-controlled unmanned mobile device that is operable in either of two modes. The device has a rotor assembly that allows it to vertically take off and land, to fly to a selected site and then hover. The device walks on legs that extend from the device for a ground mode of operation, and retract for a flying mode of operation.
U.S. Pat. No. 7,959,104 to Kuntz discloses a combination UAV/UGV comprising a vehicle body with front and rear rotors mounted on each side of the body about corresponding rotational axes. Each rotor has an annular covering attached to the tips of the rotor blades such that the covering essentially forms a wheel with the rotor blades acting as the spokes. The rotors are movable from a flying mode, where the rotational axes are oriented vertically such that the rotating rotors provide lift, to a ground mode where the rotational axes are oriented horizontally and the body is supported on the annular covering, and the rotating rotors act as wheels to move the body along the ground.
A problem with the Kuntz vehicle is that in ground mode, the wheel treads will often pick up debris which unbalances the rotor/wheel assembly and which can make the vehicle unable to fly. Also the annular covering increases the mass that must be rotated for flight. Further since the annular covering spins with the rotors, any contact with walls or the like during flight can damage the rotor. Even slight contact can slow the rotor such that control is difficult, and can also upset the balance of the rotor and adversely affect flying.